The present invention relates to a current-type converter protecting apparatus and particularly to an apparatus suitable for protecting a current-type converter from occurrence of an overvoltage due to employment of self-extinction elements in the converter.
Generally, as a system for converting AC power into DC, there have been used voltage-type converters and current-type converters.
Recently, various trials have been carried out for improving a power factor or the like by using self-extinction elements in such converters. For example, a voltage-type converter employing self-extinction elements has been proposed in U.S. Pat. No. 4,361,866, etc.
On the other hand, various current-type converters employing self-extinction elements have been proposed. In such current-type converters, however, there is a problem that an overvoltage is caused when a current is cut off. Protection of a current-type converter from such an overvoltage is discussed in a paper by Yoshioka et al, "PWM GTO CONVERTER OF NEW COMMUTATION ENERGY SYSTEM" (The Institute of Electrical Engineers of Japan, Semiconductor Power Conversion Society, Material SPC-84-60). In this paper, insufficient consideration has been made into a point of how to protect main circuit elements of the current-type converter from an overvoltage caused across a DC reactor provided at the output side of the converter, when an erroneous turn-off pulse is mixed at any point in time into a gate signal due to noises or the like. This is because the protecting apparatus disclosed in the above paper is for overvoltage suppresion and energy feeding back in commutation of the main circuit current and it cannot cope with an overvoltage caused in any point in time, so that the period in which an overvoltage can be suppressed is limited to the time of commutation. Further, in the conventional converter protecting apparatus, there has been another problem that the arrangement of the protecting apparatus is complicated because a diode bridge, capacitors, self-extinction elements are used.